MacBook Pro 13 i5 for Logic Express?

I have been using Logic Express for over a year now, with a late 2007 white MacBook, Core 2 duo 2.0ghz, which I upgraded ram to 4GB and the hard drive to 500GB.
Over the past few months, I have gotten more and more into au instrument plugins, like EZ Drummer, Kontakt and Reaktor, often all on the same songs, and my system is struggling to handle it. The projects are taking longer to load initially and playback is often stuttering or blanking out.

My question is if I upgrade to the a new MacBook Pro 13 inch i5, 2.4 GHz with 4GB of ram and 500 GB hard drive, while i see a noticeable improvement in using Logic Express?

I have an external monitor I use, so I am not interested nor can I afford the 15 inch model.

I am wanting some advice on whether upgrading will really help my workflow, or if I should just continue to suffer through it using my current setup/